Direct access storage system having plural interfaces which permit receipt of block and file I/O requests

ABSTRACT

A storage system includes a storage controller and storage media for reading data from or writing data to the storage media in response to SCSI, NFS, CIFS, or HTTP type read/write requests. The storage controller includes SCSI, NFS, CIFS, and HTTP interface adapters for receiving the read/write requests and effecting the reading of data to or the writing of data to the storage media.

[0001] The present application is a continuation of application Ser. No.09/829,470, filed Apr. 9, 2001, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to data processingsystems, and particularly to a direct access storage system with acombined block interface and file interface access.

[0003] Interconnecting the various elements of a processing system(e.g., processor units and peripheral equipment such as direct accessstorage devices) permits the resources of the system to be distributedso that they are available to all elements of the system. For example,multiple processor units may be connected to a storage system forsharing not only the afforded storage space, but the files that arestored there. Typically, a network architecture of one type or anotherwill be used to implement the interconnection, which may dictate theparticular of interface structure between the elements of a system,e.g., a processor unit and a data storage system. For example, it hasbeen popular to connect stand-alone processor units to direct accessstorage devices using a small computer standard interface (SCSI). SCSIconnections use block transfer protocols in which a logical unit number(LUN) identifies the logical volume for access.

[0004] Network protocols, on the other hand, are different. Protocols ofchoice for networked and distributed processing systems included NetworkFile System (“NFS;” an open operating system developed by SunMicrosystems), a Common Internet File System protocol (“CIFS;” a remotefile access protocol), or a HyperText Transport Protocol, more popularlyknown as “HTTP.” These protocols use what is known as a “file systeminterface,” and while the file interface structures used to implementthe different file system interface protocols, they use a common filesystem structure. Thus, data stored on a storage system using a filesystem interface of two or more types are available to all host systems.For example, a storage system capable of handling input/output requestsof both NFS and CIFS protocols, i.e., an NFS protocol interface and aCIFS protocol interface, can store data files that are accessible tohost processors having either of the NFS interfaces. That is, a hostsystem with only an NFS interface can access and open files stored by ahost system with a CIFS interface, and the host system with a CIFSinterface can access and open files stored by the system via the NFSinterface—provided the storage system has both interfaces.

[0005] Storage systems having one or more of the file system interfacesof the types described above provide access through an I/O read or writerequest that includes a file name, and an lock request that seeks aright to access the particular file of the I/O request.

[0006] Most direct access storage systems have either a block interfaceor a file interface, and host systems using a block interface protocolcannot access storage systems employing file interface protocols.Further, because of the differences between block and file interfacestructures and the way data is stored and accessed, a storage system isstructured for a block system or a file system, but not both.

SUMMARY OF THE INVENTION

[0007] The present invention provides a storage system with directaccess storage devices that can be shared between a block interface anda file interface. The invention provides a system architecture with bothblock and file interfaces to realize high performance, scalability, andavailability.

[0008] According to the present invention a storage system includes aplurality of physical disk units, a host processing system that mayinclude a number of processing units, and a controller element thatincludes a SCSI interface adapted to receive block type read/writerequests and at least one file system interface adapted to receive I/Oread/write file requests. The file system interface may be compatiblewith a network file system (NFS), a Common Internet File System (CIFS)protocol or HyperText Transfer Protocol (HTTP), or any combination offile system protocols. The controller element operates to connect theprocessor units of the host processing system to the plurality ofphysical disk units. The controller unit uses logical volume management,allowing the different block and file system I/O requests to accessportions of the physical disk units allocated for block system data orfile system data.

[0009] In an alternate embodiment of the invention, file system datastored on the physical disk units is made accessible to a block systemrequest by performing a volume backup, thereby permitting data sharingbetween a SCSI interface and a file system interface. A number ofadvantages are achieved by the present invention. First, is that directaccess storage device (“DASD”) resources can be shared between thoseprocessing elements having only a block interface, and those processingelements having a file system interface or multiple file systeminterfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a block diagram illustration of processing system thatincludes a storage system constructed according to the teachings of thepresent invention;

[0011]FIG. 2 is a block diagram broadly depicting the SCSI interfaceadaptor shown in FIG. 1;

[0012]FIG. 3 is a block diagram broadly depicting a files systeminterface adaptor as shown in FIG. 1;

[0013]FIG. 4 is a block diagram that illustrates a drive interfaceadaptor as shown in FIG. 1;

[0014]FIGS. 5 and 6 illustrate two types of logical volume status tablesas used in connection with the present invention;

[0015]FIG. 7 illustrates a file interface adaptor according to analternate embodiment of the invention; and

[0016]FIG. 8 is an alternate embodiment of a SCSI interface adapter foruse in the storage controller of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Turning now to the figures, and first to FIG. 1, there isillustrated a processing system 10 that includes a host system 12coupled to a storage system comprising a storage controller 14 and aplurality of physical disk units 20 (20 ₁, 20 ₂, . . . , 20 _(n)) thatare managed by the storage controller 14.

[0018] Although not specifically shown, the host system 12 most likelywill comprise a plurality of processor units, although it could alsocomprise a single processor unit with multiple I/O interfaces, includinga block system interface and at least one file system interface. Itshould be understood, therefore, that the host system howeverimplemented will include at least one SCSI protocol type interface (forblock system file transfers with the storage controller 14) and at leastone file system interface, such as an interface or interfaces thatoperate according to NFS, CIFS, and/or HTTP protocols. Accordingly, thehost system may comprise multiple processor units, one having an SCSIinterface, another with an NFS interface, still another with a CIFSinterface, and so on. Alternatively, the host system may be implementedby a single processor unit having all four (SCSI, NFS, CIFS, and HTTP)type interfaces.

[0019] As FIG. 1 shows, the host system will include, according to anaspect of the present invention, a backup utility 12 a, shown in phantomin FIG. 1, a common library system library data structure 12 b. Theseprogrammatic elements are included in that portion of the host system 12having the SCSI type interface to implement said aspect of theinvention. They are described more fully below.

[0020] The host system 12 is coupled to the storage controller 14 by abus structure 16. For reasons that will become clearer below, the bussystem 16 may be multiple bus structures to connect the host system tocorresponding ones of four interface adaptors 26-32 of the storagecontroller 14.

[0021] As FIG. 1 shows, the storage controller 14 includes four types ofinterface adaptors: a SCSI interface adaptor 26, a NFS interface adaptor28, a CIFS interface adaptor 30, and a HTTP interface adaptor 32. Eachis configured to handle a specific protocol. Accordingly, the SCSIinterface adaptor 26 is configured to receive, from the host system 12,SCSI or block system protocol type input/output requests. As isconventional, a block system protocol request will include a logicalunit number, a block identification (ID) within the specified logicalunit, and data link. File system protocol requests, depending upon type,are received by the NFS, CIFS, and/or HTTP interface adaptors 28, 30,32. File system protocol requests will typically utilize an upper layerprotocol of TCP/IP that includes an identification of a specific filename rather than a logical unit number.

[0022] The storage system 14 may have any number of any type of theinterface adapters 26-32. For example, a storage controller 14configuration may include two (2) SCSI interface adaptors 26, one (1)NFS interface adaptor 28, three (3) CIFS interface adaptors 30, and two(2) HTTP interface adaptors 32. Alternatively, another storagecontroller 14 configuration may have just four interface adapters, oneof each type, with the capability of having more adapters of any typeadded. As can be seen, a variety of other alternative storage controllerconfigurations are possible. By providing the storage controller 14 withsuch a flexible architecture, high scalable performance and highavailability is achieved. This, in turn, provides a storage systemcontroller 14 with the capability of increasing, for example, the numberof NFS interface type adapters according to performance demands placedupon the storage system by the host system 12. Moreover, by providingthe storage controller 14 with multiple interface adapters of the sametype (e.g., NFS interface adapters) a failure of one still leaves theother or others of that same type to execute the requested processingfrom the host system.

[0023] Continuing with FIG. 1, the various adaptors 26, . . . , 32 ofthe storage controller 14 connect to drive interface adaptors 46, onefor each physical disk unit 20, through a system bus 36A, 36B, and aconnecting facility 40. The connecting facility is basically an arbiterthat functions to arbitrate communicative access between the variousinterface adaptors 26, . . . , 32 and the drive interface adaptors 46.In addition the connecting facility 40 will also arbitrate access forthe interface adaptors 26, . . . , 32 to the cache memory 42.

[0024] Although FIG. 1 shows only one drive interface adapter 46 foreach physical disk unit 20, in order to provide fault tolerantcapability, as well as increased performance, the physical disk units20, or any of them, may have two or more drive interface adapters 46servicing them. Each disk unit is connected to an interface adapter by aconnection 50.

[0025] The storage controller 14 also includes a terminal interfaceadaptor 43 to provide a system administrator with access to the storagecontroller for configuration purposes, as will be discussed more fullybelow.

[0026] Referring now to FIG. 2, there is illustrated in block diagramform the SCSI interface adaptor 26. The SCSI interface adaptor 26, asare the file system and drive interface adaptors 26, 46 (FIGS. 3 and 4),are illustrated in terms of the major functions performed by each. Itwill be evident to those skilled in this art that the functional aspectsof the adaptors 26, 28, and 46 may be implemented in a variety of knownways such as, for example, with programmed microprocessors andassociated support circuitry, state machines, or a combination of suchconstruction with or without additional circuitry.

[0027] As FIG. 2 shows, the SCSI interface adaptor 26 will include anSCSI interface function and circuitry configured to be coupled to acompatible SCSI interface of the host system 12. The SCSI interfaceadaptor 26 operates to receive I/O read or write requests from the hostsystem 12, and to communicate responses back to the host system 12. Forthat purpose, the SCSI interface adaptor 26 includes a SCSI interfacefunction 60 for handling the protocol needed for SCSI datacommunication.

[0028] As will be seen, the storage controller 14 employ a logicalvolume management in order to share the resources of the physical diskunits 20 between block system and file system interfaces. Accordingly,the SCSI interface adaptor includes a logical volume access blockfunction 64 that is configured to convert the LUN of a I/O read writerequest to a logical volume access. Also included in the SCSI interfaceadapter 26 is a drive interface adaptor (DIA) interface function 66 tohandle the communication colloquy with the drive interface adaptors 46in response to information provided by the logical volume access block64. A conventional cache manager function 68 manages data access of theSCSI interface adapter 26 to the cache memory 42 by the SCSI interfaceadaptor 26.

[0029] The NFS interface adaptor 28 is functionally illustrated in FIG.3. The other file system interface adapters, i.e., the CIFS and HTTPinterface adapters are functionally equivalent to the NFS interfaceadapter, with the exception of the process block 72, so that thedescription of the NFS interface adapter 28 will apply equally to theCIFS and HTTP interface adapters 30 and 32 unless otherwise noted. AsFIG. 3 shows, the NFS interface adaptor includes a TCP/IP interfacefunction 70 for handling I/O requests and responses thereto between thestorage controller 14 and an NFS interface of the host system 12according to the communications protocols incorporated in TCP/IP. Aprocess block 72 operates to interpret the NFS features of an I/O reador write request, and formulates the responses thereto for communicationto the host system 12 (FIG. 1). For a CIFS or HTTP interface adapter,the process block function 72 would need to be configured to accommodatethe particular protocol. A common file system function block 73 includesa command process function 74, a logical volume address converterfunction 76, and a lock manager function 78. The common file systemfunction block 73 will receive an I/O read or write request from theTCP/IP interface function 70, convert the file interface information ofthe request to block interface information, and pass the block interfaceinformation to a logical access function 82 (which is substantially thesame as that of the SCSI interface adapter 26). Then, the logical volumeaccess function 82 forwards that request to a logical volume that mapsto a portion of the physical storage space implemented by the physicaldisk units 20.

[0030] As did the SCSI interface adaptor 26, the NFS interface adaptor28 includes a cache manager function 84 for managing accesses to thecache memory 42 (FIG. 1) and a drive interface adapter (DIA) function 86for handling data communication with a drive interface adaptor 46.

[0031]FIG. 4 illustrates the functional features of a drive interfaceadaptor 46. As FIG. 4 shows, the drive interface adaptor 46 will includea host interface adapter (DIA) interface function 100 to handlecommunication with a particular interface adaptor 26, 28, . . . , 32. Alogical/physical address conversion function 102 converts logicaladdresses received from the logical volume access block functions of theinterface adapters (e.g., logical volume access block 64 of the SCSIinterface adaptor 26, or the logical volume access blocks 64 in eitherof the NFS, CIFS, or HTTP interface adaptors 28, 30, 32). If a redundantarray of inexpensive disk (RAID) architecture is implemented, thelogical/physical address conversion function 102 will operate to managethat architecture, handling the mirroring of data in the case of a RAID1 architecture, for example, or controlling the data striping employedin a RAID architecture.

[0032] A cache manager function 106 of the drive interface adaptor 46manages data accesses with the cache memory 42. A Read/Nrite controlfunction 104 handles the actual data flow, pursuant to a read or a writerequest, between the drive interface adaptor 46 and the associatedphysical disk unit 20.

[0033] Operation of the system of FIG. 1 in connection with a blocksystem I/O request is generally as follows. Block system I/O read orwrite requests will be received by the SCSI interface adaptor 26 on aSCSI bus 16 a (FIG. 2). Such requests, as indicated above, will have aLUN which includes a block ID in the specified LUN and a data length asis conventional. The request will be received by the SCSI interfacefunction 60 and passed to the logical volume access block function 64.If the request is an I/O read request, the logical volume accessfunction will first check, through the cache manager 68, to see if therequested data resides in the cache memory 42 (e.g., from a prior readrequest for the data, or from a prior write of the data to the physicaldisk units 20). If so, the logical volume access block function 64 willaccess the cache memory 42 for the block identified in the I/O readrequest, and forward it to the SCSI interface function 60. The SCSIinterface function 60, in turn, will forward the requested data to thehost system 12. If, however, the requested block does not exist in thecache memory 42, the logical volume access block will send a request,through the DIA interface 66, to the HIA interface 100 of the driveinterface adaptor 46 for the physical storage 20 whereat the requesteddata block resides. The SCSI interface adaptor will then wait for aresponse, performing other processing as necessary.

[0034] If, on the other hand, the I/O request received from the hostsystem 12 is a write request, the logical volume access function 64 willsend the data block received with the request to the cache memory 42.Then, the logical volume access function 64 will, through the DIAinterface function 66, send a write request to appropriate the driveinterface adaptor 46, identifying the location in the cache memory 42 atwhich the data block to be written resides. The drive interface 46 willthen access the cache memory 42 for the data block, and write it tophysical storage 20.

[0035] File system requests are received by one of the file systeminterfaces: either the NFS, the CIFS, or the HTTP interface adapter,depending upon whether the source is a NFS, CIFS, or HTTP interface ofthe host system 12 and, therefore, one of the three protocols filesystem protocols: that is, NFS, CIFS, or HTTP. File system I/O requestsmay be accompanied by lock/unlock requests. A lock request seeks accessto a specific data block within a specific file, or the file itself. Anunlock request releases access to the block/file previously obtained. Asis conventional, an lock or unlock request will include either the filename of the file sought to be accessed, or a block number in thespecified file, and a block length. Alternatively, the request mayinclude a file name and additional information identifying the right toaccess the file.

[0036] Control information for lock/unlock processing is stored in thecache memory 42 for the each of the protocols used by the file systeminterface adaptors 28, 30, 32, although other shared memory can be usedif available.

[0037] File system I/O requests issued by the host system 12 arereceived by the TCP/IP interface function of the file system interfaceadaptor to which the request is directed. (That is, if an NFS hostinterface issues the request, the request will be received by the NFSinterface adaptor 28. Similarly, for CIFS or HTTP host interfaces, therequests will be received by the CIFS or HTTP interface adaptors 30, 32respectively. The requests will all, thereafter be handled in basicallythe same way as described hereinafter.) The TCP/IP interface function 70will receive the request and pass it to the appropriate process functionblock 72 for further processing.

[0038] The process function block 72 will convert the received requestto one for a common file system, and pass the converted request to thecommon file system function block 73 where it is received by a commandprocess function 74 and transferred to a logical volume addressconverter function 76.

[0039] If the request is a lock request, it will also be passed to thelock manager function 78, which checks to determine whether or notaccess to the requested file is available. If access is available, thelock manager function 78 will initiate a reply (“access granted”) to theprocess function block 72. The process function block 72 will thennotify the host system 12 of the access grant via the TCP/IP interfacefunction 70. Generally, the locking protocol is specified in NFS, CIFS,or HTTP level. If, on the other hand, access is not available, forexample being locked by another request, the lock manager function 78will so notify the process function 72, which will send a request tohost system 12 to pend the lock request. When the lock request issubsequently made available by release of the lock by the other request,the lock manager 78 will notify the host system 12 that access isgranted.

[0040] I/O read or write requests from a file system interface of thehost system 12 will include a file name, a block number in the specifiedfile, and a block link. Read and write requests travel through theTCP/IP interface function 70, the process function block 72 and thecommand process function 74, to the logical volume address converter 76.There, the information in the request is converted to a logical volumeunit number, a block number in the logical volume, and a logical blocklength. The logical address converter 76 will then pass this informationto the logical volume access function block 64 which, as did the logicalvolume access function block 64 of the SCSI interface adaptor 26, willhandle the data transfer in the same way; that is, if it is a readrequest, the logical volume access function block 82 will check to seeif the requested information resides in the cache memory 42 and if so,retrieve the information and return it to the host system 12 in responseto the request. If the requested information does not reside in thecache memory 42, the logical volume access function block 82 will issuea request to the appropriate drive interface adaptor 46, requesting thatthe information be retrieved from the physical storage 20. Writerequests are also handled in the same manner as described aboverespecting the logical volume access block 64 of the SCSI interfaceadapter.

[0041] The drive interface adapters 46 will operate in the same mannerwhen responding to read or write requests, regardless of the interfaceadapter issuing the request. It will execute read/write operations toand from the physical storage 20 in response to requests received fromthe interface adapters 26, . . . , 32. The drive interface adapters 46preferably have the capability of performing write after processing fromcache memory 42. (Write after processing is typically used, for example,in connection with mirrored storage. A write request will be processedby writing the data of the request to a specific physical storage unit20. Subsequently, the same data, which may be stored in the cache memory42, can be written to whatever disk storage unit (or units) 20 used formirroring the data.)

[0042] Referring to FIG. 4, requests are received at the drive interfaceadapter 46 through the HIA (host interface adapter) interface function100. Requests will include a logical-physical address that maps to anaddress in the physical storage 20 managed by the drive interfaceadapter 46. Conversion of the received logical-physical address to anaddress of physical storage 20 is performed by the logical/physicaladdress conversion function 102, which may also be structured to executewrite after processing if, for example, RAID architecture thatimplements mirroring is used, e.g., RAID 1.

[0043] The configuration of logical volumes may be established by asystem administrator through a work station (not shown) connected to thestorage controller 14 (FIG. 1) through the terminal interface 43. Thesystem administrator may create data structures, for example in the formof the table 120 illustrated in FIG. 5. Each entry 122 ₁, . . . , 122_(m) of the table 120 corresponds to a logical volume established by thesystem administrator. And, each entry 122 contains informationdescribing the logical volume, including the mapping to the physicalstorage space 20. In addition, each entry 122 may contain anidentification as to whether or not it is for a block system interfaceor a file system interface.

[0044] Logical volumes allow the physical storage 20 to be allocatedbetween a block system and a file system as needed. For example, a firstportion of the physical storage 20, say, one-third of the storage, maybe allocated to block system data storage. Then, the remaining physicalstorage may be allocated to storing data for file system protocols.Later, it may be determined that less block system storage is actuallyneeded so that the allocation could be changed, for example, somethingless than originally allocated, say one-fourth of the physical storage20. The remaining physical storage 20 dedicated to file system storageis concomitantly increased.

[0045] Typically, logical volumes for a file system interface (e.g., theNFS or CIFS interface adapters 28, 30) will include file managementinformation required by the common file system function block 73. Thisfile management information provides the basis for the logical volumeaddress conversion performed by the logical volume address converter 76of the common file system block 73. Logical volume information for blocksystem interface, i.e. the SCSI interface adapter 26, typically do nothave such information, making it very difficult to access a logicalvolume for a block interface from a file interface. Therefore, in orderto preclude unnecessary errors, status information can be included ineach entry 122 for the logical volume, identifying whether that volumeis a file system or a block system logical volume. Thus, as FIG. 5illustrates, the entry 122, for logical volume 1 contains information toidentify it as a block system logical volume, whereas the entry 122 ₂for logical volume 2 contains information identifying it as a filesystem logical volume.

[0046] There is, however, a way, according to the present invention, ofaccessing a logical volume for a file system from a block systeminterface, such as the SCSI interface adaptor 26. According to thisaspect of the invention, that portion of the host system 12 having aSCSI interface is provided with a backup utility 12 a (FIG. 1) that,when running, can issue a volume backup request to the SCSI interfaceadaptor 26 of the storage controller 14.

[0047] This will cause the entire logical volume identified in therequest to be read from the physical storage 20, from the first addressto the last address of the logical volume, without consideration ofmanagement information. The same portion of the host system 12 is alsoprovided with the common file system library 12 b, which provides theability to recognize the file management information of the common filesystem function 73. Thereby, the host system 12 can access an arbitraryfile on a logical volume for a file system from an interface of a blocksystem. (Thus, by using a common file system library, the host system 12to access a file on a logical volume for a file interface through ablock system interface (e.g., a SCSI interface, since a common filesystem library can recognize the file management information of thecommon file system function 73,)

[0048] In order to provide at least a modicum protection againstinadvertent or other access of file system data from a block systeminterface or adapter, the logical volume table information could includeinformation respecting whether or not the particular logical volume isaccessible to certain types of access. For example, a file systemlogical volume would include information that it was or was notaccessible from a block system access. Thus, as indicated in FIG. 6, thelogical volume table entry 132 ₁ for logical volume 1 containsinformation identifying it as a file system volume, inaccessible to ablock system access. Conversely, the entry 132 ₂ indicates that logicalvolume 2 is also a file system volume, but it is accessible to a blocksystem access. Similarly, the entry 132 _(M) for volume M is also a filesystem logical volume, accessible to a block system access. The entry132 _(J) is, on the other hand, a block system logical volume.

[0049] Turning now to FIG. 7, there is illustrated an alternateembodiment of the invention. The storage controller 14 of FIG. 1 isillustrated as having three separate file system interface adapters 28,30, and 32, one each to NFS, C1FS, OR CIFS type protocols. However, asFIG. 7 illustrates, the storage controller 14 may alternatively have acommon file system adapter 140 for handling all three file systemprotocols (i.e., NFS, CIFS, or HTTP) in a single interface adapter 140.As shown, I/O and other requests from the host system 12, whether NFS,CIFS or HTTP, are received by a TCP/IP interface function 142. TheTCP/IP interface determines the particular communication protocol andpasses the request to the appropriate one of the process function blocksincluding NFS process block 144, CIFS process block 146 and HTTP processblock 148. From there, processing proceeds as described above. Similarto, for example, FIG. 3 the single interface adaptor 140 includes acommon file system function block 150 which includes a command processfunction 152, a logical volume address converter function 154 and a lockmanager function 156. Further, similar to FIG. 3, the single interfaceadaptor 140 includes a logical volume access function block 158, a cachemanager function block 160 and a DIA interface function block 162. Forenhanced reliability and faster access to the physical disk units 20,the storage system 14 may include multiple interface adapters 140.

[0050] Turning now to FIG. 8, there is a further embodiment of theinvention illustrated. In this embodiment, the SCSI interface adapter,designated with the reference numeral 26′, includes the logical/physicaladdress conversion/RAID control function 102′, that was contained in thedrive interface adapter 46 (FIG. 4) of the embodiment illustrated inFIG. 1. Similarly, the NFS, CIFS, and HTTP interface adapters 28, 30, 32could also have the logical/physical address conversion 102′ included inthem, thereby removing that function from the drive interface adapters46. Alternatively, if the file system interface adapter 140 shown inFIG. 7 is used, that could also include the logical/physical addressconversion 102′.

What is claimed is:
 1. A storage system for handling input/output (I/O)requests from a plurality of processors, wherein a first processor ofthe processors sends block I/O requests and a second processor of saidprocessors sends file I/O requests, comprising: a storage mediaincluding a plurality of disk units; a bus coupled to said storagemedia; a cache memory, coupled to said bus, storing data in response tosaid block I/O requests and said file I/O requests; and a plurality ofinterfaces, coupled to said cache memory, to be coupled to said firstand second processors, wherein a first interface of said interfaces,coupled to said first processor, receives block I/O requests from saidfirst processor to access a first portion of said storage media, andwherein a second interface of said interfaces, coupled to said secondprocessor, receives file I/O requests to access a second portion of saidstorage media.